Here,
this might help. The recommendations for June 2011 should be on their way, so keep an eye out for those.
1. If you really want to stick to your budget, then a
Radeon 5770 a.k.a 6770 is your card. The 6770 is just a re-badged 5770, so no point buying one if the price is any higher.
2. If you can stretch a bit, I would suggest the NVIDIA
GTX 460 768MB or the
Radeon 6790.
I know that it's not on the recommended buy list, but if you look at the last page of the article - GPU Hierarchy, and have a look at the prices on Newegg, I think you'll find that the Radeon 6790 and GTX 460 768MB offer great value for a teeny bit more. I kinda like NVIDIA - CUDA, PhysX and all that - but it's your call. Here are some reviews:
http://www.tomshardware.com/reviews/radeon-hd-6790-barts-gpu-geforce-gtx-460,2917.html
http://www.guru3d.com/article/radeon-hd-6790-review/1
http://www.bit-tech.net/hardware/graphics/2011/04/05/amd-radeon-hd-6790-1gb-review/1
http://www.techpowerup.com/reviews/AMD/HD_6790/1.html
I'd say that the GTX 460 768MB narrowly beats the Radeon 6790, no?
3. And if you're quite elastic, the
Radeon 6850 offers tremendous bang-for-buck, but is quite expensive.
One thing to keep in mind is that MSI and EVGA manufacture great cards while XFX have a (double) lifetime warranty on theirs. Some EVGA cards also have a lifetime warranty as well, but they're usually hi-end ones. Sapphire is also good, but not in my top 3 list. That winds up my rhetoric. Good luck!